What are the Zwolle and PAMI‑II criteria for determining eligibility for early discharge after primary percutaneous coronary intervention for ST‑segment elevation myocardial infarction?

Zwolle and PAMI-II Criteria for Early Discharge After Primary PCI in STEMI

The Zwolle score (≤3 points) is the recommended clinical tool to identify low-risk STEMI patients who can be safely discharged 48-72 hours after primary PCI, incorporating six predictors: age, Killip class, post-procedural TIMI flow grade, three-vessel disease, anterior infarction, and ischemic time. 1

Zwolle Risk Score Components

The Zwolle Primary PCI Index assigns points based on the following mortality predictors 1, 2:

• Age (continuous variable contributing to score)
• Killip class at presentation (I-IV)
• Post-procedural TIMI flow grade (0-3)
• Three-vessel disease (presence/absence)
• Anterior MI location (yes/no)
• Ischemic time (symptom onset to reperfusion)

Low-risk patients are defined as those with a Zwolle score ≤3, who demonstrate 30-day mortality rates of 0.1-0.2% and can be discharged within 48-72 hours. 3, 4 The score has been externally validated with excellent discriminative power (C-statistic 0.907-0.937) and identifies approximately 62-73% of STEMI patients as low-risk. 3, 5, 4

PAMI-II Criteria

While the evidence focuses primarily on the Zwolle score, PAMI-II criteria similarly identify low-risk patients suitable for early discharge and are mentioned alongside Zwolle as validated risk stratification tools. 2, 6 Both scoring systems reliably stratify patients for safe early discharge decisions. 2

Mandatory Clinical Stability Requirements for Early Discharge

All patients being considered for early discharge must meet these absolute criteria, regardless of risk score 1, 2:

• No ongoing ischemia or recurrent chest pain 1, 2
• No acute kidney injury 1
• No left ventricular dysfunction (LVEF >45%) 1, 2
• No heart failure (Killip class I) 1, 2
• No procedural complications (vascular injury, bleeding) 1, 2
• Hemodynamic stability without vasoactive or mechanical support 2, 6
• No persistent arrhythmias on telemetry monitoring 2, 6
• Adequate ambulation tolerance without symptoms 2, 6
• Adequate post-discharge support and proximity to medical care 1, 2

Discharge Timing Algorithm

24-48 Hours (Very Early Discharge - Highly Selected Patients Only)

Consider discharge at 24-36 hours only for patients who meet ALL of the following 2:

• Zwolle score ≤3
• All standard low-risk criteria satisfied
• Live within approximately 20 km of the PCI center
• No arrhythmias on continuous monitoring
• Reliable post-discharge support and follow-up arranged
• Adequate ambulation demonstrated

48-72 Hours (Standard Early Discharge - Low-Risk Patients)

This is the recommended discharge window for low-risk patients (Zwolle score ≤3) who meet all clinical stability requirements. 1, 2 The 2025 ACC/AHA guidelines specifically endorse this timeframe, noting that early discharge <3 days is not associated with increased mortality in appropriately selected patients. 1

>72 Hours (Extended Hospitalization Required)

Patients with ANY of the following high-risk features require hospitalization beyond 72 hours 2:

• Zwolle score >3
• Killip class II-IV heart failure
• LVEF <40-45%
• Anterior wall STEMI with large territory involvement
• Three-vessel disease
• Prolonged ischemic time (>3 hours from symptom onset to reperfusion)
• Post-procedural complications (acute kidney injury, bleeding, vascular injury)
• Planned staged revascularization

Monitoring Requirements

All STEMI patients require a minimum of 24-48 hours of telemetry monitoring with duration determined by cardiac risk. 1 The 2025 ACC/AHA guidelines provide a Class I recommendation for telemetry monitoring to reduce cardiovascular events. 1

Continuous arrhythmia and ST-segment ischemia monitoring should be initiated immediately and continue uninterrupted for ≥24-48 hours. 1 For low-risk patients after successful revascularization, ST-segment monitoring may be discontinued after 12-24 hours if clinical stability is maintained, though arrhythmia monitoring should continue. 1

Pre-Discharge Checklist (Mandatory for All Patients)

Before any discharge, ensure completion of 2:

• Optimized secondary prevention medication regimen with patient education completed
• Confirmed cardiology follow-up appointment within 7-14 days
• Assurance of access to prescribed medications at discharge
• Written action plan for chest pain or cardiac symptom management
• Enrollment in cardiac rehabilitation program (Class I recommendation)

Common Pitfalls to Avoid

The most frequent errors leading to inappropriate early discharge include 2:

• Inadequate time allocated for medication education and warning sign recognition
• Failure to appropriately up-titrate secondary prevention medications before discharge
• Unreliable or absent post-discharge follow-up arrangements
• Lack of social support assessment or residence far from medical facilities
• Discharging patients with subtle clinical instability

Weekend and holiday discharges are associated with longer length of stay due to reduced staffing; proactive discharge planning on weekdays improves efficiency. 5 Patients requiring warfarin at discharge have significantly longer hospitalizations (7.6 vs 4.6 days), and those transferred back to presenting hospitals rather than discharged directly from the PCI center also experience prolonged stays (5.6 vs 4.0 days). 5

Enhanced Risk Stratification

Adding LVEF assessment to the Zwolle score improves risk stratification accuracy. 7 Patients with LVEF <50% have significantly longer hospital stays (3.1 vs 2.1 days) and ICU stays (36.5 vs 24.0 hours) compared to those with LVEF ≥50%, even when Zwolle scores are similar. 7 The combined model (Zwolle + LVEF) demonstrates superior predictive performance compared to Zwolle score alone. 7

Transthoracic echocardiography should be performed on all STEMI patients prior to discharge to assess LV function, detect mechanical complications, and guide therapy. 1

Real-World Implementation

Despite validation of early discharge criteria, only 8-28% of eligible low-risk patients are actually discharged within 72 hours in practice. 5, 8 Structured discharge planning with early risk stratification using validated tools significantly improves adherence to appropriate discharge timing without compromising safety. 8, 4

The negative predictive value of Zwolle score ≤3 for 30-day mortality is 100% (95% CI 97.0-100%), meaning no deaths occur in properly identified low-risk patients. 4 In contrast, high-risk patients (Zwolle >3) have 30-day mortality rates of 12.4-19.7%. 5, 4